Molten metal bath level maintenance system

ABSTRACT

The level of molten metal in a molten metal coating furnace is controlled by the use of a counterweighted hollow ceramic displacement block having thin walls not subject to spalling. The hollow ceramic immersion block is associated with a bath level control system having a fail safe feature.

United States Patent [1 1 Padjen et al.

[ June 12, 1973 MOLTEN METAL BATH LEVEL MAINTENANCE SYSTEM [75]Inventors: George Padjen; Robert W. Helman; Joseph A. Brugger, all ofBethlehem, Pa.

[73] Assignee: Bethlehem Steel Corporation,

Bethlehem, Pa.

[22] Filed: Dec. 28, 1971 [21] Appl. No.: 213,144

[52] US. Cl. 118/2, 73/3225, 118/5, 118/8,118/12,118/420,118/421 [51]Int. Cl. B05c ll/l0 [58] Field of Search 118/7, 4, 8, 9, 10,

118/12, 5, 2, 423, 425, 419, DIG. 18, 420,

DIG. 19, 421, 429; 117/114 A, 114 B, 114 C,

[56] References Cited UNITED STATES PATENTS 418,801 1/1890 Lorimer118/429 12/1919 Lutz 118/405 X 1,926,122 9/1933 Stenhouse 65/164 X2,914,423 11/1959 Knapp 118/125 X 3,060,055 l0/1962 Bixler 118/405 X3,079,889 3/1963 Jacobs et al. 118/8 3,227,577 l/l966 Baessler et al....1 18/405 X 3,368,525 2/1968 Sacre 118/7 X 3,510,345 5/1970 Marchant...118/7 X 3,522,836 8/1970 King ll8/7 X 3,599,600 8/1971 Carleton et a1.118/8 Primary Examiner-Morris Kaplan Attorney-Joseph J. OKeefe [57]ABSTRACT The level of molten metal in a molten metal coating furnace iscontrolled by the use of a counterweighted hollow ceramic displacementblock having thin walls not subject to spalling. The hollow ceramicimmersion block is associated with a bath level control system having afail safe feature.

7 Claims, 2 Drawing Figures MOLTEN METAL BATH LEVEL MAINTENANCE SYSTEMBACKGROUND OF THE INVENTION The present invention relates to the coatingof linear material with molten metal coatings and particularly toprecise and effective control of the bath level of a molten metalcoating bath.

In stepped types of molten metal coating pots, and also on occasion inother molten metal coating apparatus, it is frequently desired toprecisely and quickly control the bath level in the coating section ofthe pot. Various means have in the past been used to control the bathlevel such as molten metal pumps and other devices. One means forcontrolling the bath level as' well as for detecting the bath level of amolten metal bath has been by the use of ceramic blocks immersed withinthe bath. When used for controlling the bath level such blocks arecustomarily referred to as displacement blocks. By driving thedisplacement block into the bath the level of the bath will be raised asthe block displaces the metal. Conversely by withdrawing thedisplacement block from the molten metal the level of the bath may belowered. Such displacement blocks have usually consisted of a solidblock of a heat resistant ceramic material such as a high aluminarefractory or graphite. The block is normally quite sturdy because ofits solid construction. Nevertheless extreme difficulty has beenexperienced with cracking and spalling of such blocks over a long periodof use. Pieces tend to spall off such blocks contaminating the moltenmetal bath and at times threatening to stop up any orifices in thecoating pot under the surface of the bath such as the die orifices or,even more detrimentally, induction heating passageways in the bottom orsides of the molten metal pot thus interfering with the uniform heatingof the molten metal. In addition the temperature of the molten bath hasoften been detrimentally affected by the use of the solid ceramic blockto control the level of the molten bath. As the ceramic block is driveninto the molten bath the mass of the block often acts as a heat sink toextract heat from the bath. Thus the molten bath will often suffer asudden small but significant cooling as its level is increased. This hasled to difficulties in maintaining a uniform bath temperature. Similardifficulties have not usually been encountered where a ceramic block orfloat has been used as a bath level indicator rather than a bath levelcontroller because the float in this case maintains a substantiallyconstant level in the molten bath.

It has also at times been a problem in molten metal heating furnaces orpots where the material to be coated enters the bath through a die inthe bottom of the pot, or under the surface of the bath, when the linearmaterial such as wire or the like suddenly breaks. In such case the wireor the like may pull out of the die and the molten metal may flowthrough the die out of the coating pot causing damage not only to thedie but also to the surroundings.

SUMMARY OF THE INVENTION The foregoing disadvantages and problems of theprior art practices have now been obviated by the herein describeddiscovery of the present applicants. The present applicants havediscovered that if a hollow ceramic displacement block having relativelythin outer walls is immersed in a molten metal coating bath it will havea greatly decreased tendency to crack and spall in comparison with asolid ceramic displacement block and will also not tend to distort theheat balance within the molten bath as it moves during adjustment of thebath level. The hollow ceramic displacement block, because of its muchdecreased mass, does not provide the large heat sink of a solid blockwhich extracts heat from the bath and the thin walls of the hollow blockcan easily adjust to changes in temperature and quickly come to auniform temperature without cracking and spalling of the ceramic. Asolid ceramic block on the other hand takes a significant period of timeto reach an equilibrium temperature after every change of the level ofthe block in the molten bath and the cooler internal and upper portionsof the block are subject to significant temperature differences andtemperature induced physical stress in relation to the outer and lowerportions of the block. In other words as a solid block begins to heatup, the outer sections of the block tend to expand and attempt to pullaway from the cooler inner core of the block while as the block beginsto cool the outer portions of the block tend to shrink with relation tothe hotter core and the core of the block thus has a tendency to splitthe outer portions. All this temperature induced stress tends to causespalling and cracking of a solid immersion block.

The hollow ceramic displacement block of the present invention on theother hand has only a small mass so that it does not significantlyaffect the heat balance of the molten bath and its thin walls are notsubjected to high differential rates of cooling and heating and thus arenot subject to cracking and spalling.

The present inventors have also, using their durable immersion blockdevised a failsafe type bath level control system which will lower thebath level of a molten coating bath quickly if longitudinal materialpassing through the bath should break. Thus molten metal is preventedfrom escaping from the bath through the die orifice if the wire escapesfrom the die. The buoyancy of the hollow ceramic block aids in quickwithdrawal of the block from the molten coating bath.

Also if the coating equipment is shut down and the operator shouldthrough oversight neglect to lower the bath level the failsafe featurewill serve to lower the bath level instantly thus avoiding needlesserosion of the wire by the hot bath and the necessity for restringingthe wire before restarting.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic elevation of amolten metal coating bath apparatus incorporating the improvements ofthe present invention.

FIG. 2 is an enlarged broken away section of the hollow immersion blockshown in FIG. 1 showing the construction of the block.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1 there is shown amolten metal coating pot 11 having a lining of refractory brick 13.Induction heating tubes 15 positioned in the bottom of the bath aresurrounded by an induction coil 17. On one side of the coating pot 11there is a shelf 19 which provides a shallow section 21 of a bath 23 ofa molten metal such as aluminum, zine, copper or like. In the bottom ofthe shelf 19 or shallow section 21 of the bath 23 there is positioned ahousing 25 containing a die 27 through which a wire 29 enters thecoating pot 11. A screw cap 31 secures the die 27 within the housing 25.Preferably the die 27 will be composed of a metal or ceramic materialnon-wettable by the molten metal which composes the bath 23. Within thecoating pot 11 there is supported from piston rod 33 and a wire cable 35a hollow ceramic displacement block 37. The block 37 will desirably havevents 38 in its upper surface. The piston rod 33 is attached to a piston39 contained in a large pneumatic or, if desired, hydraulic cylinder 41which serves to drive the displacement block 37 into the molten bath 23when it is desired to raise the level of the bath from its lowest level,shown by the dotted line 43, to a higher level sufficient to submergethe die 27 beneath the surface of the bath, for instance, at the levelshown by the line 45. In some cases it may be found that a hydrauliccylinder will provide more precise control of the bath level system. Thecable 35 secured at one end to the hollow displacement block 37 passesover the sheaves 47 and 49 and is attached at its opposite end to acounterweight 51 heavy enough to lift the hollow ceramic displacementblock 37 entirely from the bath 23 when not opposed by the action of thepneumatic or hydraulic piston and cylinder 39 and 41. Stops 52 and 53within the cylinder 41 restrict the travel of the piston 39 so that theblock 37 cannot be driven too deeply into the molten bath 23 and so thatports, referred to hereinafter, in the upper portion of the cylinder 41are not closed off by upward movement of the piston 39. At one side ofthe coating pot 11 opposite the shelf 19 there is a recess 54 in theside of the pot 11, which recess 54 accommodates a ceramic float 55which is buoyed up by the molten metal of the bath 23 and detects thelevel of the bath 23 when it is at its higher levels. The float 55 maybe composed of either a hollow or a solid ceramic block. Since the levelof the molten metal customarily remains at the same level on the float55, it is not subject to great fluctuations in temperature and thus doesnot have a tendency to crack or spall due to differential rates ofcooling and heating. The use of a solid ceramic block for the float 55is thus not detrimental. The movement of the float 55 is transferred toa rod 57 and then to fulcrum arm 59 pivoted on support 60. Arm 59 has acontact and pointer 61 on the end which rides over the contacts of apotentiometer 63 attached to one pole of a source of current 65. Thecontact 61 taps off a potential from the potentiometer 63 and conductsit via flexible lead 66 to a suitable controller 67. The other pole ofthe current source 65 is also attached to the controller 67 through thelead 69. The controller 67 will have suitable internal circuits to applya current through leads 71 and 73 to solenoid 75 to move a fluid controlvalve 77 to apply more or less pneumatic or other pressure from an airor other pressure source 79, usually comprising a standard compressedair line in the shop, through an inlet 81 to the cylinder 41 to controlthe position of the piston 39 in the cylinder and thus the position ofthe hollow displacement block 37. The valve 77 may either apply more orless pressure to the cylinder 41 from compressed fluid source 79 or maybleed off fluid from cylinder 41 through exhaust port 83 depending uponerted by a spring 85 which biases the solenoid in the oppositedirection.

The wire 29 passes from some previous treating or other operation, notshown, passes over a guide sheave 87 and downwardly to a lower guidesheave 89 which changes the direction of the wire and passes it upwardlythrough the die 27 to guide sheave 91 which in turn directs the coatedwire away from the coating pot 11 to a takeup block 92 or,alternatively, to some other treating operation, not shown. Between theguide sheaves 87 and 89 the wire 29 passes over a contact sheave 93which steadies the wire against the thrust of a biasing sheave 95 whichis mounted upon the end of a piston rod 97 secured to a piston 98 in apneumatic or other fluid pressure cylinder 99. The biasing force appliedby the biasing sheave 95 against wire 29 is provided by fluid pressureapplied against the piston 98 from a pressure source 101. A pneumaticpressure source will usually be found to be very satisfactory for thispurpose. The air or other pressure from the source 101 is regulatedthrough the use of pressure regulator 103 by adjustment of knob 105 andis then applied via conduit 107 to junction 109 where the pressure isdirected through two separate conduits 111 and 113 to cylinder 99 and toa control cylinder 115 respectively. The pressure applied to the piston98 in cylinder 99 will bias sheave 95 against the wire 29 with aconstant force which will be resisted by the tension in the wire. Thetension exerted by the wire 29 against the sheave 95 serves to maintainthe piston 98 above an exhaust port 117 in the side of the cylinder 99.The pneumatic pres sure applied to control cylinder 115 is applied tothe surface of a piston 119 within the cylinder 115 and serves to forcethe piston 119 back against the force of a compression spring 121 untilexhaust outlet 123 from cylinder 115 and exhaust outlet 125 fromcylinder 41 to control cylinder 115 are blocked off or closed by thepiston 119.

The desired bath level 45 to be maintained by the controller 67 may beindicated to the controller by a set point potentiometer 126. Aswitch127 is included in the circuit of potentiometer 126 to activate ordeactivate the circuit. A second switch 128 serves to activate thecontroller 67 from a power source 129 through the coils 131 of atransformer 133.

A second coil 135 of transformer 133 serves upon the closing of a switch137 to activate the coils 17 of the induction heated pot 11 through asuitable controller 139. A third coil 141 of transformer 133 serves toapply power through a switch 143 and controller 145 to the wire takeup92 through leads 147 and 149.

A branch 151 from exhaust outlet 125 leads to a pressure safety releasevalve 153 which may be adjusted to open at various pressures byadjustment 155. If the pressure within the cylinder 41 should becomeexcessive for some reason, possibly through the failure of the control67, tending to drive the hollow block 37 too forcefully or too far intothe molten bath the pressure safety release valve 153 will open untilthe excessive pressure is relieved.

In FIG. 2 there is shown enlarged and broken away to illustrate apreferred construction, a hollow ceramic displacement block 157 similarto the displacement block 37 of FIG. 1. The hollow block has a steel orother metal or heat resistant structural material inner framework 159,which, as shown, may take the form of metal box 161 is preferably madeof stainless steel because this alloy has a lower coefficient ofexpansion and is more resistant to the molten bath. The end of thepiston rod 163 is secured to the box 161 through a structural web 165welded to the inside of the box 161. A series of studs 167 are weldedover the surface of the box 161 and to the end of the studs 167 thereare welded transverse sections of metal lath 169 spaced about onequarter to one third of an inch from the surface of the box 161. Themetal lath 169 is completely covered by a plastering of a high aluminaor other suitable type of ceramic plaster 171 over and around the latheto completelycover the surface of the hollow box 161. The ceramicplaster 171 may be any suitable proprietary refractory composition,preferably having a high alumina composition, particularly if the moltenbath 23 is comprised of molten aluminum. Such a plaster composition iscommonly used for patching or molding in and about ceramic heatingfurnaces. A typical anslysis would be 93.4 percent A1 0 5.8 percent P 0,(used as a binder) and less than 1 percent residual or contaminatingelements. It is advantageous for the hollow ceramic block to be open atthe upper end as shown in H6. 2 so that there may be a free transfer ofheat to the atmosphere by convection from the inside of the block. Anopen end in addition allows a slightly freer expansion of the refractoryplaster 171 along the major length dimension of the block.

In the operation of the bath level control of the coating apparatusshown in FIG. 1, after the activation of switches 127 and 128, thedesired level 45 of the molten bath 23 is set on the referencepotentiometer 126 causing the controller 67 to operate the solenoid 75to adjust the pneumatic valve 77 until pneumatic pressure admitted tocylinder 41 from source 79 is sufficient to drive the hollow ceramicdisplacement block into the bath 23 sufficiently to bring the level 45of the molten bath 23 to a point where the ceramic float 55 transmits asignal to controller 67 through the various mechanical linkages of thefloat 55 and the potentiometer 63 indicating that the correct level asdetermined by the setting on potentiometer 126 has been attained. Thecontroller 67 will thereupon control the valve 77 to maintain sufficientpressure in cylinder to maintain the hollow ceramic block 37 at thecorrect level and to adjust the level of the bath by adjusting the levelof the hollow displacement block if the level of the bath varies for anyreason.

As the wire 29 passes over the guide sheaves 87 and 89 and contactsheave 93 the tension in the wire opposes the thrust of the contactsheave 95 occasioned by the piston 98 acted upon by the pneumaticpressure from the source 101 as adjusted by pressure regulator 105. Theexhaust port 117 in cylinder 99 is thus closed off by the piston 98. If,however, the wire 29 should break so that it may pull out of the die 27and possibly release the bath metal through the empty die orifice, themovement of contact sheave 95 is no longer opposed and the piston 98will abruptly move downwardly exposing the exhaust port 117 and allowingthe pressure in the conduit 111, junction 109 and conduit 113 to drop.Upon the drop in pressure in conduit 113 the pressure in cylinder 115will also drop and the compression spring 121 will force-the cylinder119 downwardly, opening the exhaust outlets 123 and 125 and allowing thepressure within the cylinder 41 to drop precipitously. As the pressurein the cylinder drops the action of the counterweight 51 combined withthe buoyancy of the block quickly pulls the hollow displacement blockfrom the molten bath 23 thereby quickly dropping the level of the bathbelow the level of the die 27 so that no molten metal from the bath 23has a chance to escape from the coating pot 11. The buoyancy of thehollow ceramic displacement block considerably facilitates the speedywithdrawal of the block from the molten bath.

If the electrical or pneumatic fluid pressure systems in FIG. 1 shouldfail due to a failure, for instance, in power source 129, thecompression springs on solenoid 75, or 121 in cylinder 115, will actrespectively to open the exhaust ports 83 or to exhaust the pressurefrom cylinder 41 and allow the counterweight 51 to quickly raise thehollow ceramic displacement block 37 from the molten bath 23 to preventthe making of off gauge wire or the freezing of the wire 29 in the die27 if the electrical power for the takeup block 92 pulling the wirethrough the bath should fail or be interrupted. Likewise if the powersource 129 should fail cutting off the induction heating of the coatingpot, the hollow ceramic block will be immediately withdrawn from themolten bath to prevent it from freezing into the bath.

Likewise if the operator should shut down the control apparatus byoperating switch 128 at the end of a run or for some other reason thehollow ceramic block will be automatically withdrawn from the coatingbath. It will readily be recognized that switches 137 and 143 could beeasily ganged together to operate as a unit so that opening of any ofthe switches will cause withdrawal of the block.

The sudden changes in the immersion of the hollow displacement block 37within the molten metal do not cause any cracking and spalling of theblock because while the thin built up walls of the block are exposed tosudden extremes in temperature they are not differentially heated andcooled across any significant thickness of material so that the materialof the wall quickly comes to an equilibrium temperature no matter whatits position within the hot molten bath may be.

The reinforcing of the thin walls of the displacement block by the metalbath is also a considerable aid in enabling the ceramic to withstandrepeated heating and cooling cycles.

It will be understood that various means to detect breakage of the wire29 or failure of the power to any of the parts of the apparatus, eitherelectrical or pneumatic, could be used in place of the apparatus shown.For example, a gravity type electrical contact switch could withsuitable circuits be used to detect breakage or loss of tension in thewire 29. Likewise various alternative means could be devised to exhaustthe pressure from the cylinder4l to allow the block to be raised fromthe coating pot.

We claim: I

1. A bath level maintenance system for a molten metal coating apparatuscomprising:

a. a ceramic pot for a molten metal coating bath havi. a reservoirsection for the maintenance of a reservoir of molten coating metal, and

ii. a coating section having a wire entrance die spaced at an elevatedposition with respect to the bottom of said reservoir section,

b. a thin walled hollow ceramic surfaced displacement member arrangedfor adjustable positioning within said reservoir section to determinethe level of the molten bath with respect to said wire entrance die,

c. a first control means to move said ceramic displacement means intoand out-of said molten bath to maintain a desired level of molten metalover said wire entrance die, and

d. counterweight means secured to said ceramic displacement member tolift said member from said molten bath if said fluid control means failsto maintain control.

2. A bath level maintenance system for a molten metal coating apparatusaccording to claim 1 wherein said ceramic displacement member comprisesa metal underframe with a ceramic outer coating molded over the surfacethereof.

3. A bath level maintenance system for a molten metal coating apparatusaccording to claim 2 wherein said metal underframe comprises a boxmember having lath affixed to the surface thereof and an outer highalumina ceramic coating molded thereabout.

4. A bath level maintenance system for a molten metal coating apparatusaccording to claim 1 additionally comprising:

e. detector means to detect the tension in wire pass- 8. ing throughsaid molten coating bath, and

f. second control means to activate said first control means of (c) toquickly raise said ceramic displacement member and lower said bath levelbelow the orifice of said wire entrance die upon the detection by saiddetector means of (e) of a sudden loss of tension in the wire passingthrough said molten coating bath.

5. A bath level maintenance system for a molten metal coating apparatusaccording to claim 5 additionally comprising adjustable means to limitthe force which can be exerted upon said ceramic displacement member bysaid first control means to limit the depth into the molten coating bathwith respect to the surface thereof to which the ceramic displacementmember can be driven.

6. A bath level maintenance system according to claim 5 additionallycomprising means to activate said control means of (c) to initiatewithdrawal of said block from said molten bath upon interruption of thepower for heating said molten bath.

7. A bath level maintenance system according to claim 6, additionallycomprising means to activate said control means of (c) to initiatewithdrawal of said block from said molten bath upon interruption of thepower for passing said wire through said bath.

1. A bath level maintenance system for a molten metal coating apparatuscomprising: a. a ceramic pot for a molten metal coating bath having i. areservoir section for the maintenance of a reservoir of molten coatingmetal, and ii. a coating section having a wire entrance die spaced at anelevated position with respect to the bottom of said reservoir section,b. a thin walled hollow ceramic surfaced displacement member arrangedfor adjustable positioning within said reservoir section to determinethe level of the molten bath with respect to said wire entrance die, c.a first control means to move said ceramic displacement means into andout of said molten bath to maintain a desired level of molten metal oversaid wire entrance die, and d. counterweight means secured to saidceramic displacement member to lift said member from said molten bath ifsaid fluid control means fails to maintain control.
 2. A bath levelmaintenance system for a molten metal coating apparatus according toclaim 1 wherein said ceramic displacement member comprises a metalunderframe with a ceramic outer coating molded over the surface thereof.3. A bath level maintenance system for a molten metal coating apparatusaccording to claim 2 wherein said metal underframe comprises a boxmember having lath affixed to the surface thereof and an outer highalumina ceramic coating molded thereabout.
 4. A bath level maintenancesystem for a molten metal coating apparatus according to claim 1additionally comprising: e. detector means to detect the tension in wirepassing through said molten coating bath, and f. second control means toactivate said first control means of (c) to quickly raise said ceramicdisplacement member and lower said bath level below the orifice of saidwire entrance die upon the detection by said detector means of (e) of asudden loss of tension in the wire passing through said molten coatingbath.
 5. A bath level maintenance system for a molten metal coatingapparatus according to claim 5 additionally comprising adjustable meansto limit the force which can be exerted upon said ceramic displacementmember by said first control means to limit the depth into the moltencoating bath with respect to the surface thereof to which the ceramicdisplacement member can be driven.
 6. A bath level maintenance systemaccording to claim 5 additionally comprising means to activate saidcontrol means of (c) to iniTiate withdrawal of said block from saidmolten bath upon interruption of the power for heating said molten bath.7. A bath level maintenance system according to claim 6, additionallycomprising means to activate said control means of (c) to initiatewithdrawal of said block from said molten bath upon interruption of thepower for passing said wire through said bath.